1. Field of the Invention
The present invention relates to an impact absorbing member for a vehicle. More specifically, the invention relates to the impact absorbing member which hardly falls laterally when it receives an impact load from a front or back of a vehicle obliquely, and which is prevented from impairment of impact absorbing performance.
2. Description of the Related Art
An impact absorbing member for a vehicle is mounted to a frond end portion or the like of a vehicle to absorb an impact load applied to the vehicle. One example thereof is an impact absorbing member having a tubular body portion with a closed section formed of a plurality of plate-like side walls. Some of the plurality of side walls are formed a concave groove(s) which is recessed inwardly of the tubular body portion and which extends parallel to an axial direction thereof. This impact absorbing member is disposed between a vehicle body side member and a bumper member such that the axial direction thereof is directed in a fore and aft direction of the vehicle. When the impact absorbing member receives a compressive load, it collapses like bellows axially to absorb the impact energy (see, e.g., Patent Document 1: WO 2005/010398).
FIGS. 6A and 6B are drawings explaining one example of such impact absorbing member for vehicle. FIG. 6A is a schematic plan view showing a bumper beam 10 of a vehicle front side and vicinity thereof, as viewed from an upper side of a vehicle. Right and left side members 12R and 12L are provided with crash boxes 14R and 14L, as the impact absorbing members, respectively at front ends thereof. The bumper beam 10 is fixed at right and left ends thereof to the crash boxes 14R and 14L. FIG. 6B is a section along a line VIA-VIA in FIG. 6A, that is a section view near a right mounting portion. The crash box 14R includes a main body portion 20 having a tubular shape and a pair of mounting plates 22 and 24 integrally weld-fixed to both ends of the main body portion 20 in the axial direction, respectively. The crash box 14R is fixed to the side member 12R and the bumper beam 10 via the mounting plates 22 and 24 with a bolt (not illustrated) or the like.
FIGS. 7A and 7B are drawings specifically explaining one example of the main body portion 20 of the crash box 14R, in which FIG. 7A is a perspective view, and FIG. 7B is a front view. A section (corresponding to FIG. 7B) perpendicular to the axial direction of the main body portion 20 has an elongated shape (in FIG. 7B, flat octagonal shape elongated in an upper-lower direction) as a basic shape, which has a pair of parallel long sides each obtained by linearly interpolating two sides adjacent to a concave groove 32. A pair of wide side walls 30 constituting the long sides of the basic shape are each provided with, at an intermediate portion (a central portion in FIG. 7) in the width direction thereof, i.e., the upper-lower direction in FIG. 7A and FIG. 7B, concave grooves 32 which are recessed inward of the main body portion 20 and extend parallel to the axial direction respectively. The crush box 14R is disposed between the side member 12R and the bumper beam 10 such that the pair of the wide side walls 30 are spaced in the vehicle width direction. The main body portion 20, comprised of a polygonal tube with a closed section having a elongated shape in the upper-lower direction, is obtained by integrally weld-fixing a pair of press plates 26 and 28 bent into an M shape, with mutually superposing both side edges of one press plate on both side edges of the other press plate.
When this crash box 14R receives a compressive load F giving an impact on a front of the vehicle, the main body portion 20 collapses like bellows as shown in FIG. 6C. The crash box 14R absorbs by deformation thereof the impact energy to relieve the impact applied to structural members of the vehicle such as the side member 12R and the like. The bellows-like collapse (L-shaped folds in FIG. 6C) is a phenomenon in which the main body portion 20 is buckled continuously at multiple places. The collapse usually starts from a side of the bumper beam 10, i.e., an input side, and progresses toward a side of the vehicle body with time. The bumper beam 10 has left-right symmetrical shape, and a left mounting portion is similarly structured.
The bumper beam 10 functions as a reinforcement (reinforcing member) and a mounting member for a bumper, and a bumper main body 16 made of synthetic resin or the like is integrally mounted on the bumper beam 10. The bumper beam 10 corresponds to the bumper member, and the side members 12R and 12L correspond to the vehicle body side members, of the present invention.
By the way, in recent years, as a crash test for evaluation of damage on the vehicle, a test method is adopted in which an oblique barrier is used to assume collision of the vehicle in an oblique direction. According to a test shown in FIG. 8A, a vehicle is offset-collided at a predetermined vehicle speed V1 (e.g., 15 km/h) with a rigid barrier 42 having a crash surface 40 inclined at a predetermined angle θ1 (e.g., about 10°). According to a test shown in FIG. 8B, a crash cart 46 provided with a barrier 44 at its front end is collided at a predetermined speed V2 (e.g., 15 km/h) with a corner of a vehicle in a direction inclined at a predetermined angle θ2 (e.g., about 10°).
According to such test methods, for example, a load F is applied obliquely to the vehicle to generate a moment load M in the crash box 14R as shown in FIG. 9, and the crash box 14R tends to fall laterally toward an inner (center) side (a left direction in FIG. 9) of the vehicle. As a result, desired impact-energy absorbing performance of the crash box 14R may not be obtained.
To solve this problem, Patent Document 2 (JP2002-155981A) proposes an impact absorbing member for a vehicle having a tubular shape with a square closed section, in which concave grooves are not provided in the side walls, but flanges projecting radially outward from plate-like side walls or corners of the square closed section are provided.
Accordingly, applying the technology described in the Patent Document 2 to the impact absorbing member for the vehicle whose side walls are provided with the concave grooves described in the Patent Document 1 may be conceivable, which is however unknown yet. In this case, the flanges projecting radially outward are to be provided on corners or a flat parts of the side walls. With this, even when the impact load is applied to the impact absorbing member in the oblique direction of the vehicle, the impact absorbing member will be prevented from falling laterally, and can render a predetermined impact absorbing performance. However, due to disposition of the flanges projecting radially outward, the impact absorbing member occupies a large space in the vehicle to impair mountability thereof on the vehicle.